There has been proposed a technique for performing near field communication between apparatuses using RFID (Radio Frequency Identification). In such near field communication, a communication distance between a reader/writer and an RFID tag is different depending on a communication standard of the near field communication. As the communication standard of the near field communication, there are three types: Type A, Type B, and Type F currently. Since modulation systems and the like are different in the respective communication standards, optimum matching conditions for antennas are different.
Usually, matching conditions for antennas of the reader/writer and the RFID tag are fixed in advance. Therefore, when a reader/writer and an RFID tag corresponding to a plurality of communication standards communicate, if the matching conditions are adjusted to one communication standard, it is likely that a communication distance cannot be sufficiently secured in the other communication standards.
The communication distance between the reader/writer and the RFID tag are also different according to whether a voltage is applied from an external power supply. Further, depending on the type of the antenna of the reader/writer, a matching condition is sometimes different from a matching condition for the antenna of the RFID tag. Furthermore, manufacturing fluctuation is present in the RFID tag. A resonance frequency changes according to the manufacturing fluctuation and affects a communication distance.
For example, Patent Literature 1 discloses that a variable capacitive element of a resonance circuit tuning system is adjusted in order to detect at least one of an electric current and a voltage of an antenna coil and change resonance impedance of the antenna coil on the basis of the detection.
In Patent Literature 1, the capacitive element is adjusted using a voltage value of the antenna coil. However, the frequency of a carrier wave and the frequency of a data modulation signal are greatly different depending on a communication standard. When the RFID tag is applied with a voltage from the external power supply to operate, the RFID tag does not operate with the energy of a carrier wave from the reader/writer. Therefore, the communication distance is often increased by adjusting matching of the antenna of the RFID tag to resonate at the frequency of the data modulation signal rather than the frequency of the carrier wave that maximizes the voltage value of the antenna coil.